Formation of Complexes of Flavonoids and Metals. Determination of

Molecules 2000, 5
516
Formation of Complexes of Flavonoids and Metals.
Determination of the Stoichiometry and Stability Constants
M. G. Barolli1, R. Alonso Werner2, L. D. Slep2 and A. B. Pomilio1
1
PROPLAME-CONICET, Departamento de Química Orgánica, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Pabellón 2, Ciudad Universitaria, 1428 Buenos Aires, Argentina
2
INQUIMAE, Departamento de Química Inorgánica, Analítica y Química Física, Facultad de Ciencias
Exactas y Naturales, Universidad de Buenos Aires, Pabellón 2, Ciudad Universitaria, 1428 Buenos Aires, Argentina
E-mail: grajo@quimor.qo.fcen.uba.ar
Abstract: The complexes between some flavonoids and metals (Co(II), Cu(II), Mn(II),
Mg(II), Sn(II)) have been studied by spectrophotometric methods in order to determine the
stoichiometry and stability constants.
Introduction
Flavonoids are poliphenolic compounds, which are characterized by showing a variety of pharmacological activities, e.g. antioxidant, antihelmintic, antiinflamatory, antiviral, antitumor, etc. Most of
these activities are due to their ability to inhibit enzymes, such as trypsine, protein kinases, topoisomerases.
The complex formation of these compounds and metals of the active enzyme site or complexes
between certain amino acids of the active site and the metals of the medium is probably the reason of
this enzymatic inhibition.
This study deals with the determination of the stoichiometry of the complexes of some flavonoids
and a variety of metals (Co(II), Cu(II), Mn(II), Mg(II), Sn(II)) as well as the determination of each stability constant.
Experimental
Spectrophotometric methods were used. Solutions of each flavonoid and metal salts in a molar rate
(metal mols/total mols) in the range of 0.09 and 0.9 were prepared using methanol.
UV-Visible spectra for each molar rate were performed, and plotting Absorbance vs Molar rate or
Initial metal concentration the exact stoichiometry of each complex was determined.
517
Molecules 2000, 5
Results and discussion
Formation of species with a 1:1 (metal:ligand) stoichiometry were obtained for the flavonoids
tested. The stability constant of each complex was determined.
OH
HO
OH
HO
O
HO
O
OH
OH
OH O
QUERCETIN
OH
OH O
MORIN
Acknowledgment: The authors are indebted to CONICET (Argentine) and the Universidad de Buenos
Aires for financial support.
References and Notes
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
Phytochemistry 1986, 25(2), 383-385.
Biochemical Pharmacology 1993, 46(7), 1257-1271.
J. Biol. Chem. 1996, 271(4), 2262-2270.
J. Nat. Prod. 1995, 58(6), 823-829.
Biochem. Pharmacol. 1989, 38(10), 1617-1624.
Biochem. Pharmacol. 1986, 35(14), 2345-2357.
Biochem. Pharmacol. 1986, 35(2), 237-245.
Biochem. Pharmacol. 1987, 36(5), 717-720.
Biochem. Pharmacol. 1989, 38(17), 2859-2865.
Can. J. Chem. 1991, 69, 1994-2001.